Picked up this gem for my DS once I got home from teh coll-edge. It's very fun! You play as either Lucian, this dark swordsman type dude, or Aaron, a "gunslinger". It's technically the sequel to the Boktai GBA games, but they did away with the sun sensor. Time and weather effects are now entirely in-game. You can switch between the characters with select once you get to chapter 3 (which is, like, 1 and a half hours of gameplay, TOPS, if you're slow like me).
Gameplay itself is pretty fun. It reminds me of a twist on the old Secret of Mana games. Very fun. I highly recommend it.